1. Field of the Invention
The present invention relates to a rodless cylinder having a pair of guides for bearing a load imposed on a slide table.
2. Description of the Related Art
Rodless cylinders have recently been finding wide use as workpiece feed mechanisms in factories or the like. Rodless cylinders take up a smaller installation space and can be handled more easily than ordinary cylinders with rods because the rodless cylinders have a shorter stroke of displacement. In addition, the rodless cylinders are capable of preventing dirt, dust, and other foreign matter from entering the cylinder tube more effectively than the ordinary cylinders with rods, with the result that the rodless cylinders can perform highly accurate positioning operation on workpieces which are fed by the rodless cylinders.
One typical rodless cylinder comprises a cylinder tube and a slide table which is linearly movable reciprocally under the pressure of compressed air supplied through a port. A guide is disposed between the slide table and the cylinder tube for allowing the slide table to slide smoothly with respect to the cylinder tube.
One conventional form of guide comprises a guide rail mounted on one side wall of the cylinder tube which is displaced sideways off the longitudinal axis of the cylinder tube (see Japanese utility model publication No. 4-52482).
However, the side rail mounted on one side wall of the cylinder tube as disclosed in Japanese utility model publication No. 4-52482 poses certain problems. For example, the guide rail tends to undergo an excessive load due to a load that is applied at a position spaced from the longitudinal axis of the cylinder tube by a workpiece or the like supported on the slide table or a load that is generated by a shock caused at an end of the stroke of the slide table. As a result, the durability of the guide table is relatively low, making it difficult to maintain the linearity of movement of the slide table for a long period of time.
One solution would be to use a pair of spaced linear guides of identical structure disposed between the slide table and the cylinder tube and positioned on respective opposite side walls of the cylinder tube. However, the identical linear guides are liable to interfere operatively with each other owing to manufacturing errors thereof or loads applied to the slide table. As a consequence, the linear guides soon suffer play developed in use, failing to allow the slide table to be displaced smoothly with respect to the cylinder tube in an initially intended fashion.